Pump gland packings are designed to restrict or limit leakage around a centrifugal pump’s impeller shaft. It’s commonly understood that as long as the pump gland packing leakage rate is minimal, packings are likely the most cost-effective means of containing leakage. However, in facilities with aging pumps, like many of those in the California Bay Area, the actual gland packing leakage rate is often difficult to determine.
My experience in working with petrochem refineries across Northern California leads me to conclude that gland packing leakage rates are almost always worse than imagined. Whether it’s a matter of packing gland adjustment skills, pump accessibility, aging equipment, or inability to quantify leakage, many refineries are ignoring cost savings opportunities.
Identifying gland packing that has failed can shine a light on operational issues, like inadequate flush, excessive gland load, or simply the use of the wrong packing. Unfortunately, not all refineries are taking advantage of the opportunity to make improvements. There are several reasons why controlling pump gland packing leakage rates has become a challenge.
With an increasingly younger set of engineers entering the industry, less maintenance personnel have the skills to properly install and adjust pump gland packings. Over-tightening of gland creates friction that reduces motor efficiency and accelerates packing gland deterioration, eventually leading to more leakage than anticipated.
Often, especially in older or retrofitted refineries, the pump location doesn’t facilitate frequent inspection and identification of unacceptable gland packing leakage. Some pumps operate almost entirely out-of-sight, making inspections even less likely.
Process conditions may have changed over time and exceed the design limitations of the older stuffing box and gland packing, quickly leading to gland deterioration and leakage.
Excessive leakage may go unnoticed because of rapid evaporation or absorption into the ground.
Your refinery unit may be losing revenue without knowing it. The cumulative loss of process fluid and cost—in terms of parts, labor, and downtime—of installing new gland packings in facilities with hundreds of pumps can be significant. Leakage of plant water certainly incurs costs. Leakage of hydrocarbons or revenue-producing process fluids has an even greater impact on profitability.
Even when the gland packings are working as intended, the leakage rate may be more than you imagined. Consider these points and compare them to the efficiency of a mechanical seal with a seal support system:
|
Operation |
Leakage Rate |
Compared to Mechanical Seals |
|
A properly-tightened gland packing |
Estimated to be 10 drops/minute or 0.2 gallons per day. That’s 69 gallons per year! |
Less than 0.2 US fluid ounces per hour per pair of seal faces, per API 682 Standard. |
|
High-pressure applications (15 bar) with a circumferential speed of 65 fps |
1.3 to 2.1 gallons per hour. |
Approximately 0.0016 gallons per hour. |
It may be a challenge to accurately quantify the volume of lost process fluids when gland packing leakage falls outside these expected ranges. Regardless, properly selected mechanical seals and seal support systems definitively reduce process fluid leakage. Yes, they’re more expensive than gland packings to install and they require seal support systems.
But, the long-term benefits—reducing process fluid leakage and lower on-going maintenance costs can more than justify the investment. Multiplied by dozens to hundreds of pumps in an enterprise, the long-term savings may be significant.
A review of maintenance records can uncover classes of pumps or specific pumping processes using leaking gland packings that require frequent adjustment or replacements. The initial list can be prioritized to determine the pumps prone to excessive leakage. You can then begin the process of replacing packings with appropriate mechanical seals and seal support systems.
There are dozens of mechanical seal support plans and configuration options that help ensure the reliability of the mechanical seals you select. To make the selection process easy, it’s best to work with a local mechanical seal support system vendor who’s available for on-site consulting and evaluation of your requirements.
One factor that I’ve often observed regarding the replacement of gland packings, especially those in aging pumps, is the need to consider the immediate infrastructure surrounding the pump. Limited physical space or unique piping geometry may require custom design of panels, tubing, seal pots, heat exchangers, and plant water or nitrogen supplies. A seal support system vendor who begins with an on-site analysis of your unique needs is sure to deliver solutions that simplify installation and facilitate easier maintenance.
Mechanical seal support system panels designed and configured
to meet your specific requirements.
A local vendor with in-depth industry experience will ensure each mechanical seal that replaces a leaking gland packing is matched with the API plan—process-side, dual seal, or atmospheric side—and options to reduce leakage and enhance mechanical seal reliability.
Swagelok offers more than 50 years of experience in helping Northern California industries improve the efficiency and reliability of centrifugal pumping processes. From initial on-site consultation for understanding your specific challenges to custom design and configuration of mechanical seal support systems and careful assembly with rigorous testing methods that follow ISO 9001 quality standards, Swagelok covers the full spectrum of mechanical seal support system services.
To find out more about how Swagelok Northern California can help you reduce costly maintenance and pump gland packing leakage rates using seal support systems tailored to your specific requirements, contact our team today by calling 510-933-6200.
Paul holds a B.S. in Mechanical Engineering from North Dakota State University. Before joining Swagelok Northern California, he was the West Coast Regional Sales Manager for an organization focused within the pneumatic and hydraulic industry where he supervised product distribution throughout the western United States, Canada, and Mexico. While in this role, he was able to help provide technical and application-specific expertise to customers and distribution to drive specifications.